Electrolytic cell for producing a mixed oxidant gas

ABSTRACT

An electrolytic cell for generating a mixed oxidant gas for treating bodies of water comprises an anode chamber that is defined by an anode plate at one end, a permeable membrane at an opposite end, and a first sealing gasket interposed therebetween. A cathode chamber is adjacent the anode chamber and is defined by a cathode plate at one end, the permeable membrane at an opposite end, and a second sealing gasket interposed therebetween, the first and second gaskets being separated by the permeable membrane. An anolyte reservoir is external from the anode chamber for accommodating a volume of anolyte therein, and is connected to the anode chamber to circulate anolyte thereto and to receive mixed oxidant gas therefrom. A catholyte reservoir is external from the cathode chamber for accommodating a volume of catholyte therein, and is connected to the cathode chamber to circulate catholyte thereto and to receive gas therefrom. The anolyte within the anolyte reservoir, and the catholyte within the catholyte reservoir, are each maintained at a controlled specific gravity.

REFERENCE TO COPENDING APPLICATION

This patent application is a continuation-in-part application of U.S.patent application Ser. No. 08/141,229, filed as PCT/US94/12027, Oct.20, 1994 published as WO95/11326, Apr. 27, 1995, now U.S. Pat. No.5,427,658.

FIELD OF THE INVENTION

The present invention relates generally to an electrolytic cell forgenerating via electrolytic reaction an oxidant gas comprising a mixtureof different chlorine containing species for treating bodies of water.

BACKGROUND OF THE INVENTION

The use of various types of water treatment chemicals for controllingbiological activity such as spores, bacteria, viruses, allergy, fungi,and any other biological phenomenon that adversely affects the qualityof water is well known. Chemicals added to water for the purpose ofcontrolling scaling and corrosion are also known. Such chemicals areoften used in recreational water such as swimming pools, theme parks, inindustrial or commercial process water such as cooling towers and forindustrial and municipal sewage treatment and the like, and in drinkingwater. In light of today's increased environmental awareness, the needto both minimize the types of chemicals that are routed for sewagetreatment and preserve water as a valuable resource and, therefore, theneed to maximize the use and recyclability of water used for bothindustrial and recreational applications, is greater than ever.Accordingly, in order to maximize the utility and recyclability of thewater being used in such applications it is desired that the chemicalagents used to treat the water be effective in controlling biologicalactivity, corrosion, and scaling so that the water can be reused overand over again and any blowdown water be free of noxious or toxicmaterials.

The use of chlorine for disinfecting bodies of water such as, swimmingpools, baths, reservoirs, cooling tower water, recreational water, orany form of water that is exposed to the open air, is well known. In thepast, chlorine has usually been supplied by direct application ofchlorine gas (Cl.sub. 2) from tanks containing the gas under pressure.Chlorine has also been supplied by electrolytic generation via anelectrolytic cell. Other chlorine containing gas species such aschlorine dioxide (ClO₂) have also been used in disinfecting bodies ofwater. Chlorine dioxide is a dangerous and explosive gas and is usuallyproduced as an aqueous solution at the point of usage by chemicaldecomposition of chlorine salt. Production of chlorine dioxideelectrochemically from chlorides was also unknown in the literatureprior to about 1982.

Lindstaedt U.S. Pat. No. 2,887,444 discloses a system in which a body ofwater, such as a swimming pool, is provided with a low concentration ofdissolved common salt and a stream of water is removed from the mainbody and electrolyzed to produce chlorine, and the chlorine and waterstream are returned to the main body of water.

Murray U.S. Pat. No. 3,223,242 discloses another type of electrolyticcell for generating chlorine for introduction into a stream of waterremoved from and introduced back into a swimming pool or other body ofwater.

Richards U.S. Pat. No. 3,282,823 discloses an electrolytic cell forproduction of chlorine positioned in-line for introducing chlorine intoa stream of water removed from and reintroduced into a swimming pool.

Other chlorinating systems using electrolytic cells for chlorinatingbodies of water are shown in Oldershaw U.S. Pat. No. 3,351,542, ColvinU.S. Pat. No. 3,378,479, Kirkham U.S. Pat. No. 3,669,857 and Yates U.S.Pat No. 4,097,356. These electrolytic cells are disclosed in a varietyof configurations and most of the cells utilize ion-permeable membranesseparating the anode and cathode-containing compartments.

Ion-permeable membrane technology used in electrolytic cells is welldeveloped. Ion-permeable membranes used in electrolytic cells haveranged from asbestos diaphragms to carboxylate resin polymers toperfluorosulfonic acid polymer membranes. The perfluorosulfonic acidmembranes were developed by Dupont for use in electrolytic cells.

Dotson U.S. Pat. No. 3,793,163 discloses the use of Dupontperfluorosulfonic acid membranes in electrolytic cells and makesreference to U.S. Pat. Nos. 2,636,851; 3,017,338, 3,560,568; 3,4696,077;2,967,807; 3,282,875 and British Pat. No. 1,184,321 as discussing suchmembranes and various uses thereof.

Walmsley U.S. Pat. No. 3,909,378 discloses another type of fluorinatedion exchange polymer used in membranes for electrolytic cells forelectrolysis of salt solutions.

Further discussion of membrane technology used in electrolytic cells maybe found in Butler U.S. Pat. No. 3,017,338, Danna U.S. Pat. No.3,775,272, Kircher U.S. Pat. No. 3,960,697, Carlin U.S. Pat No.4,010,085 and Westerlund U.S. Pat. No. 4,069,128.

Use of perfluorosulfonic acid membrane is also discussed in thetechnical literature, e.g. Dupont Magazine, May-June 1973, pages 22-25and a paper entitled: "Perfluorinated on Exchange Membrane" by Grot,Munn, and Walmsley, presented to the 141st National Meeting of theElectrochemical Society, Houston, Tex., May 7-11, 1972.

The structure of electrodes used in electrolytic cells is set forth thepreviously listed patents. Additionally, the following patents showparticular configurations of anodes or cathodes used in such cells.

Giacopelli U.S. Pat. No. 3,375,184 discloses an electrolytic cell withcontrollable multiple electrodes which are flat plates in electroplatingcells.

Lohreberg U.S. Pat. No. 3,951,767 discloses the use of flat plateelectrolytic anodes having grooves along the bottoms thereof forconducting gas bubbles generated in the electrolytic process.

Andreoli U.S. Pat. No. 565,953 discloses electroplating apparatus havinga plurality of metal screens which are not connected in the electriccircuit and function to plate out the metal being separated by theelectrolysis.

In "The ClO₂ content of chlorine obtained by electrolysis of NaCl,"Electrochemical Technology 5, 56-58 (1967) Western and Hoogland reportthat ClO₂ is not produced in the electrolysis of NaCl in the absence ofchlorates.

Sweeney U.S. Pat. No. 4,256,552 discloses an electrolytic generator forchlorination of swimming pools, water systems, etc., in which a bipolarelectrode is positioned in an anode compartment between an anode and ancation-exchange membrane in the wall separating the compartments.

Sweeney U.S. Pat. No. 4,334,968 discloses improvements on the cell orgenerator of U.S. Pat. No. 4,256,552 and discloses the production ofchlorine dioxide in the cell.

Sweeney U.S. Pat. No. 4,248,681 discloses a method of producingchlorine/chlorine dioxide mixtures in the cells of U.S. Pat. Nos.4,256,552 and 4,334,968 and gives some optimum operating conditions.

Sweeney U.S. Pat. No. 4,308,117 discloses a cell having threecompartments, with an anode and cathode in the outer compartments and abipolar electrode in the central compartment. A cation-exchange membraneis positioned in the wall between the central compartment and thecathode compartment, while an anion-exchange membrane is positioned inthe wall between the central compartment and the anode compartment.

Sweeney U.S. Pat. No. 4,324,635 discloses a cell having an anodecompartment, a cathode compartment, and a separating wall comprising acation-exchange membrane therein. The cell includes a pump forcirculating some of the cathode solution from the cathode compartment tothe anode compartment for pH control.

Sweeney U.S. Pat. 4,804,449 discloses an electrolytic generatorcomprising an anode compartment, a cathode compartment, at least onewall separating the anode and cathode compartment comprising an ionexchange membrane therein, and at least one bipolar electrode positionedeither in the anode or cathode compartment.

It has been discovered that an optimum degree of control over biologicalactivity, scaling, and corrosion may be realized by using a gascomposition comprising a mixture of chlorine gas and chlorine dioxidegas. The electrolytic devices disclosed in the above-referenced patentsare concerned mainly with the generation of chlorine gas viaelectrolytic reaction. Many of the above-referenced patents generate thechlorine gas using a batch-type operation rather than a continuous-typeoperation. The use of a batch-type system is known to cause variationsin the composition of the gas species produced as the concentration ofthe electrolyte changes during use, ultimately limiting theeffectiveness of such systems. Additionally, many of the electrolyticcells known in the art operate in an electrically inefficient manner dueto their construction, requiting a large input of voltage to bothovercome the internal resistance of the electrolytic cell and achieve,the desired electrochemical reaction.

It is, therefore, desirable that an electrolytic cell be constructed ina manner that will allow the generation of a mixed oxidant gascomprising chlorine and chlorine dioxide in a predetermined ratio toeffect maximum control of biological activity, scaling, and corrosion ina body of water. It is desirable that the electrolytic cell beconstructed in a manner facilitating the generation of the chlorine gasand chlorine dioxide gas in a preferred proportion without variations insuch proportion during the operation of the electrolytic cell.

It is desirable that the electrolytic cell be constructed in a mannerwhich promotes high electrical efficiency, thereby utilizing energy moreefficiently in achieving the desired electrolytic reactions andproducing the desired gases. It is desirable that the electrolytic cellbe constructed in a manner that facilitates its operation and service inthe field. It is also desirable that the electrolytic cell beconstructed in a manner that is practical from both a manufacturing andan economic viewpoint.

SUMMARY OF THE INVENTION

There is, therefore, provided in practice of this invention aneletrolytic cell for producing a mixed oxidant gas for controllingbiological activity, corrosion, and scaling in bodies of water. Theelectrolytic cell comprises an anode plate, a cathode plate, and amembrane plate interposed between the anode and cathode plate. An anodesealing gasket comprising an open cavity located at its center isinterposed between the anode plate and the membrane plate to form ananode chamber for accommodating a volume of anolyte solution. The anodesealing gasket may comprise a bipolar electrode extending across aportion of the open cavity. A second sealing gasket comprising an opencavity located at its center is interposed between the cathode plate andthe membrane plate to form a cathode chamber for accommodating a volumeof catholyte solution.

An anolyte reservoir external to the anode chamber contains apredetermined volume of anolyte and is hydraulically connected to ananolyte inlet in the anode plate for supplying the anolyte to the anodechamber. A mixed gas and anolyte outlet in the anode plate is connectedto a mixed gas and anolyte inlet in the anolyte reservoir for bothremoving the mixed oxidant gas produced in the anode chamber andcontinuously circulating the anolyte through the anode chamber. Theanolyte reservoir comprises an anolyte reservoir gas outlet for removingthe mixed oxidant gas from the anolyte reservoir and introducing it intothe body of water. The anolyte reservoir comprises an anolyte feed inletfor receiving saturated anolyte solution from an anolyte make-up tankexternal to the anolyte reservoir and anode chamber. The anolytesolution in the anolyte make-up tank is transported into the anolytereservoir by gravity. The anolyte in the anolyte reservoir istransported to the anode chamber by gravity and circulated through theanode chamber by thermal convection and the migration of the mixedoxidant gas.

A catholyte reservoir external to the cathode chamber contains apredetermined volume of catholyte and is hydraulically connected to acatholyte inlet in the cathode plate for supplying the catholyte to thecathode chamber. A gas and catholyte outlet in the cathode plate isconnected to a gas and catholyte inlet in the catholyte reservoir forboth removing the gases produced in the cathode chamber and continuouslycirculating catholyte through the cathode chamber. The catholytereservoir comprises a gas outlet for removing the gases from thecatholyte reservoir. The catholyte reservoir comprises a fresh waterinlet and means for regulating the introduction of the water formaintaining the specific gravity of the catholyte at a predeterminedlevel. The catholyte in the catholyte reservoir is transported to thecathode chamber by gravity and circulated through the cathode chamber bythe migration of the gases.

A voltage in the range of from three to ten volts is applied across theanode and cathode to effect an electrolysis reaction in the anodechamber producing a mixed oxidant gas comprising chlorine dioxide (ClO₂)and chlorine (Cl₂), and in the cathode chamber producing hydrogen (H₂)gas. The electrolysis reaction in the anode chamber is driven tocompletion by the efficient removal of H₂ gas in the cathode chamber andthe migration of sodium (Na⁺) ions from the anode chamber through apermeable membrane in the membrane plate where they react with hydroxyl(OH⁻) ions in the cathode chamber to form sodium hydroxide (NaOH). Theelectrolytic cell is able to generate a preferred composition andquantity of the mixed oxidant gas using such low voltages due to thereduced electrolyte volume in the anode and cathode chambers by reasonof the electrolytic cell construction comprising external anolyte andcatholyte reservoirs. Additionally, the use of a continuous anolyte feedsystem instead of a batch-type system permits the production of anoxidant gas having a consistent proportion of the desired mixed oxidantgas species.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome appreciated as the same becomes better understood with referenceto the specification, claims and drawings wherein:

FIG. 1 is a cross-sectional semi-schematic view of a first preferredembodiment of an electrolytic cell constructed according to principlesof invention;

FIG. 2 is a plan view of an anode plate used in the electrolytic cell;

FIG. 3 is a plan view of a sealing gasket used to construct theelectrolytic cell;

FIG. 4 is a plan view of a membrane plate comprising a permeablemembrane used to construct the electrolytic cell;

FIG. 5 is a graph illustrating an ultra-violet spectrophotometricanalysis of an anolyte solution circulated within an electrolytic celloperating at steady state conditions;

FIG. 6 is a cross-sectional semi-schematic view of an embodiment of theelectrolytic cell comprising a bipolar electrode;

FIG. 7 is a plan view of an embodiment of the sealing gasket comprisinga bipolar electrode;

FIG. 8 is a cross-sectional semi-schematic view of a second preferredembodiment of the electrolytic cell of FIG. 1;

FIG. 9 is a perspective view of a first preferred multi-electrolyticcell embodiment comprising a number of electrolytic cells constructedaccording to principles of this invention; and

FIG. 10 is a perspective view of a second preferred multi-electrolyticcell comprising a number of electrolytic cells constructed according toprinciples of this invention.

DETAILED DESCRIPTION

An electrolytic cell provided in the practice of this invention may beused for controlling biological activity, corrosion, and scaling inlarge bodies of water used in industrial and/or commercial applicationssuch as cooling towers, process water treatment, water used in foodprocessing and the like, in recreational applications such as swimmingpools, theme parks and the like, and in municipal applications such assewage treatment and disinfecting drinking water. The electrolytic cellprovides effective control of biological activity, corrosion, andscaling without the need for using supplemental chemical-type additives.The electrolytic cell does so through the electrolytic generation of anoxidant gas comprising a mixture of chlorine containing gas species thatare introduced into the large body of water.

FIG. 1 shows a first preferred embodiment of an electrolytic cellconstructed according to principles of this invention. The electrolyticcell 10 comprises an anode plate 12 comprising a generally flat sheet ofstructurally rigid material having a plurality of bolt holes (not shown)arranged around its periphery. The anode plate may be constructed fromany type of electrically conductive material that is chemicallyresistant to contact with the electrolyte and electrolysis productsproduced at the anode plate, electrochemically resistant to the actionof oxidation, and mechanically rigid such so that it may serve as astructural member for containing the electrolyte in the electrolyticcell. Suitable materials for constructing the anode plate includeniobium, columbium, zirconium, graphite, or titanium. A preferred anodeplate may be constructed from titanium. Additionally, it is desirablethat the surface of the anode plate that contacts the electrolytesolution within the cell be coated with an electrically conductivematerial. Suitable anode plate coatings include platinum, ruthenium, oriridium. Coating the anode plate with such materials is desired becausethe chemically and electrochemically resistant materials used toconstruct the anode plate are typically not good electrical conductors.Accordingly, such coating is desired in order to increase the electricalconductivity of the anode plate at the point of contact with theelectrolyte solution. In a preferred embodiment, the anode plate iscoated with ruthenium.

The anode plate may be configured in a variety of different geometricshapes such as square, rectangular, circular and the like. A preferredanode plate configuration is rectangular having a dimension ofapproximately 36 centimeters by 13 centimeters. The rectangularconfiguration is preferred because it is believed to affect the size andescape of the gas bubbles formed in the electrolytic cell chamber. Anelectrolytic cell chamber having a height greater than its widthfacilitates the formation of small gas bubbles in the electrolyte duringthe electrolysis reaction, minimizing the potential for an open circuitdeveloping at the anode surface. The anode plate may have a thicknesssufficient to provide a desired degree of structural rigidity to theelectrolytic cell. In a preferred embodiment, the anode plate has athickness of approximately two millimeters.

Moving from the anode to cathode of the cell (from left to right in FIG.1 ), an anode sealing gasket 14 is adjacent to the surface of the anodeplate 12. The sealing gasket may comprise a sheet of resilient materialhaving an open cavity 16 at the central portion of the gasket as shownin FIG. 3. The sealing gasket comprises a plurality of bolt holes 18extending around the peripheral portion of the anode sealing gasketarranged in a pattern corresponding to the plurality of bolt holes inthe anode plate. The anode sealing gasket may be made from any type ofstructurally resilient material that is electrically nonconductive, heatresistant and chemically resistant. Suitable materials for constructingthe anode sealing gasket include silicone rubber, chlorinated polyvinylchloride (CPVC), Teflon and the like. In a preferred embodiment, thesealing gasket is made from schedule 80 CPVC.

In order to promote effective sealing of the electrolyte within theelectrolytic cell, the dimensions of the anode sealing gasket may beapproximately similar to the dimensions of the anode plate. In apreferred embodiment, for a cell operating at an electrical current ofapproximately 40 amperes, the sealing gasket may have an outsidedimension of approximately 33 centimeters by 13 centimeters and the opencavity may have dimensions of approximately 25 centimeters by 6centimeters. It is desired that the anode sealing plate be slightlysmaller in length than the anode plate to facilitate electricalconnection with the upper portion of the anode plate extending from thecell, as shown in FIGS. 1 and 2.

A membrane plate 20 is adjacent to the surface of the anode sealinggasket 14. The membrane plate may comprise a sheet of a permeablemembrane material that facilitates the transfer of cations present inthe electrolyte through its surface. As shown in FIG. 4, the peripheralportion of each surface of the permeable membrane sheet may be coatedwith a resilient material 22 that is electrically nonconductive, heatresistant and chemically resistant, such as silicone rubber, Teflon andthe like. It is desirable to coat the peripheral portion of thepermeable membrane to both enhance the rigidity of the permeablemembrane sheet and to provide a non-porous surface that interfaces withthe anode sealing gasket to form an electrolyte-tight seal.

The membrane plate 20 may be configured having the same general shape asthe anode sealing gasket 14 to provide an effective seal with the anodesealing gasket to retain the electrolyte within the electrolytic cell. Aplurality of bolt holes 24 extend around the peripheral portion of themembrane plate, arranged in a pattern corresponding to the pattern ofbolt holes in both the anode plate 12 and the adjacent anode sealinggasket 14. The non-coated portion of the permeable membrane 26 maycorrespond in size and shape to the open cavity 16 in the anode sealinggasket. Accordingly, when placed adjacent to the anode sealing gasket,the non-coated portion of the permeable membrane 26 occupies an area ofthe membrane plate which corresponds in size and shape to the opencavity in the adjacent anode sealing gasket. The permeable membrane maybe made from a suitable material that would permit the transfer ofcations, such as sodium (Na⁺) ions and the like, through its surface inorder to facilitate the electrolysis reaction producing the desiredmixed oxidant gas in the electrolytic cell. Suitable permeable membranesinclude those made from an ion-permeable material sold under the tradename NAFION manufactured by DuPont Chemical, or a non-ionic modacrylicmaterial marketed under the trademark KANECARON distributed by NationalFilter Media of Salt Lake City, Utah. In a preferred embodiment, thepermeable membrane material is KANECARON. In a preferred embodiment, thesheet of permeable membrane material may have a thickness ofapproximately one millimeter.

A cathode sealing gasket 28 is adjacent to the surface of the membraneplate 20. The cathode sealing gasket may have a size and shape similarto that of the anode sealing gasket 14. Accordingly, for purposes ofsimplicity, FIG. 3 may be referred to for purposes of illustrating thecathode sealing gasket. The cathode sealing gasket comprises a sheet ofresilient material having an open cavity (similar to 16 in FIG. 3) atthe center of the gasket. A plurality of bolt holes (similar to 18 inFIG. 3) extend about the peripheral portion of the sealing gasketarranged in a pattern corresponding to the plurality of bolt holes 24 inthe adjacent membrane plate 20. The cathode sealing gasket may be madefrom the same types of resilient, chemical and heat resistant materialspreviously described for constructing the anode sealing gasket. In apreferred embodiment, the cathode sealing gasket is made from a siliconematerial.

In a preferred embodiment, the cathode sealing gasket 28 is in the shapeof a rectangle having both its outside dimensions and open cavitydimensions approximately equal to the outside dimensions and open cavitydimensions previously described for the anode sealing gasket 14.Accordingly, when placed adjacent to the surface of the membrane plate20, the open cavity of the cathode sealing gasket corresponds in sizeand shape with the non-coated portion of the permeable membrane 26.

A cathode plate 30 is adjacent to the surface of the cathode sealinggasket 28. The cathode plate may be made from a material that iselectrically conductive, chemically resistant to the electrolytesolution and electrolysis products produced within the cell, andmechanically rigid so that it can serve as a structural member to retainthe electrolyte within the electrolytic cell. Because the materialselected for the cathode plate need not be electrochemically resistant,the material has a sufficient degree of electrical conductivity that anelectrically conductive coating is not required. Since the oxidationreaction occurs at the anode and not the cathode, it is not necessarythat the material selected for the cathode plate be electrochemicallyinert. Suitable materials for constructing the cathode plate may includestainless steel 316L, stainless steel 317L, or 254 SMO stainless steel.In a preferred embodiment, the cathode plate may be made from type 316Lstainless steel.

The cathode plate may have a variety of shapes such as square,rectangular circular and the like. It is preferred that the cathodeplate be in the shape of a rectangle for the same reasons previouslydescribed for the anode plate 12. In a preferred embodiment, the cathodeplate has dimensions similar to the outside dimensions of the adjoiningcathode sealing gasket 28. Like the anode plate, the cathode platecomprises a plurality of bolt holes (not shown) extending around theperipheral portion of its surface arranged in a pattern corresponding tothe plurality of bolt holes in the adjacent cathode sealing gasket 28.The cathode plate may have a thickness sufficient to provide a desireddegree of structural rigidity to the cell. In a preferred embodiment,the cathode plate has a thickness of approximately three millimeters.

The assembly comprising the anode plate 12, anode sealing gasket 14,membrane plate 20, cathode sealing gasket 28, and cathode plate 30 formthe electrolytic cell. These elements may be fastened together by usingconventional fasteners such as bolts 32. As shown in FIGS. 1 and 2, aninsulating plate 33 may be adjacent to the surface of the anode plateopposite the anode sealing gasket to prevent an electrical short circuitfrom developing between the anode plate and cathode plate via thefastening bolts. The insulating plate may comprise a sheet ofelectrically nonconductive material having a plurality of bolt holes(not shown) located about its periphery arranged in a patterncorresponding to the plurality of bolt holes in the anode plate. Theinsulating plate is sized smaller than the anode plate, havingdimensions approximately equal to the outside dimensions of the anodesealing gasket. In a preferred embodiment, the insulating plate is madefrom polyvinyl chloride (PVC). Additionally, to prevent an electricalshort circuit between the anode and cathode plate it is desirable thatthe fastening bolts be coated or sleeved with an electricallynonconductive material.

An anode chamber 34 is formed in the electrolytic cell by the anodeplate, anode sealing gasket, and membrane plate. The anode chambercomprises a volume defined by the open cavity in the anode sealinggasket. Similarly, a cathode chamber 36 is formed in the electrolyticcell by the cathode plate, cathode sealing gasket, and membrane plate.The cathode chamber comprises a volume defined by the open cavity in thecathode sealing gasket.

The anode chamber is designed to accommodate a volume of electrolytesolution 38 that, when subjected to the passage of electricity,undergoes electrolytic reaction to produce a mixed oxidant gas 39comprising the desired proportion of chlorine containing gas species. Ina preferred embodiment, the anode chamber has a volume of approximately100 milliliters. The electrolyte solution in the anode chamber willhereinafter be referred to as the anolyte. Similarly, the cathodechamber accommodates a volume of different electrolyte solution 40 that,when subjected to the passage of electricity, undergoes electrolyticreaction to generate hydrogen in the cathode chamber. In a preferredembodiment, the cathode chamber has a volume of approximately 100milliliters. The electrolyte solution used in the cathode chamber willhereinafter be referred to as the catholyte. Although a n approximatelyvolume for the anode and cathode chamber has been disclosed, it is to beunderstood that the volume of each chamber is dependent on the spacingbetween the anode and cathode plate which, as will be described below,may vary.

A suitable anolyte may comprise any water-soluble chloride salt such assodium chloride (NaCl), potassium chloride (KCl), lithium chloride(LiCl), rubidium chloride (RbCl), cesium chloride (CsCl), ammoniumchloride (NH₄ Cl), magnesium chloride (MgCl₂), calcium chloride (CaCl₂)and the like. A suitable anolyte may also comprise a chlorite salt suchas sodium chlorite (NaClO₂) either alone or in addition to awater-soluble chloride salts. It may be desirable for the anolyte tocomprise an amount of chlorite salt because the electrolytic generationof the chloride dioxide gas (ClO₂) does not occur until chlorite ion(ClO2⁻) is present in the anolyte. In a preferred embodiment, theanolyte comprises sodium chloride (NACl). To facilitate the electrolyticreaction occurring in the anode chamber, the catholyte selected shouldreadily undergo electrolytic reaction such that its electrolysisproducts readily combine with electrolysis products of the anolyte and,thus drive the reaction in the anode chamber forming the mixed oxidantgas 39 to completion. In a preferred embodiment, the catholyte comprisessodium hydroxide (NaOH) which is formed as a reaction product betweenhydroxyl ions (OH⁻), formed via electrolysis of water molecules in thecathode chamber and sodium ions (Na⁺) formed via electrolysis of NaCl inthe anode chamber. Accordingly, the catholyte may originally be waterbut upon operation of the cell quickly undergoes electrolysis and reactsto form the hydroxide analog of the particular anolyte selected.

To minimize the internal resistance of the electrolytic cell associatedwith transferring electricity through the anolyte and catholyte volumeit is desired that the anode plate and cathode plate be spaced closelytogether. To achieve minimum internal electrical resistance the anodeand cathode plate may be spaced apart a distance in the range of fromsix millimeters to seven centimeters. As discussed below, spacing theanode and cathode plate apart within this range also facilitates thecirculation of anolyte and catholyte within the respective anode andcathode chambers. The desired spacing may be achieved by choosing thethickness of the anode and cathode sealing gaskets. In a preferredembodiment, the anode and cathode plates are spaced apart a distance ofapproximately thirteen millimeters. In such an embodiment, the anode andcathode sealing gasket would each have a thickness of approximately 6.5millimeters.

An anolyte inlet 42 is located near the lower end of the anode plateextending through the anode plate and into the anode chamber, as shownnear the bottom of FIGS. 1 and 2. The anolyte inlet can be attached tothe anode plate by conventional means such as by threaded connection,welded connection and the like. The anode inlet comprises a threadedfitting to accommodate threadable connection with an anolyte transfertube 44. The anolyte inlet is located a sufficient distance from the endof the anode plate so that it is not obstructed by the anode sealinggasket 14 for transfer of the anolyte into the anode chamber.

A mixed gas and anolyte outlet 46 is positioned at the upper end of theanode plate and extends through the anode plate and into the anodechamber, as shown near the top of FIGS. 1 and 2. Like the anolyte inlet,the anolyte outlet may be attached to the anolyte plate by theconventional connection means disclosed above. The mixed gas outletcomprises a threaded fitting for threadable connection with a mixed gastransfer tube 48.

An anolyte reservoir 50 comprises a sealed container external to theanode chamber accommodating a predetermined volume of anolyte. Theanolyte reservoir supplies anolyte to the anode chamber and receivesboth mixed oxidant gas generated in the anode chamber and anolytecirculated through the anode chamber. The anolyte reservoir and theanode chamber may be configured so that the ratio of anolyte in theanolyte reservoir to the anolyte in the anode chamber is in the range offrom 5,000:1 to 1:1. In a first preferred embodiment, the anolytereservoir has a volume of approximately one liter. Accordingly, in afirst preferred embodiment, the ratio of the anolyte in the anolytereservoir to the anolyte in the anode chamber is approximately 10:1.

The anolyte reservoir comprise an anolyte outlet 52 located at the lowerend of the reservoir that is at all times flooded with the anolyte. Theanolyte outlet is connected to the anolyte transfer tube 44 connected tothe anolyte inlet 42 of the anode plate.

The anolyte reservoir comprises a mixed gas and anolyte inlet 54 at itsupper end that is connected to the mixed gas transfer tube 48 connectedto the mixed gas outlet 46 of the anode plate. The mixed gas inlet ispositioned a sufficient distance from the top of the anolyte reservoirthat it is below the liquid level of the anolyte in the anolytereservoir. It is desirable to place the mixed gas inlet below the levelof the anolyte to facilitate both mixed oxidant gas recovery from, andanolyte circulation through, the anode chamber. Accordingly, the mixedgas enters the anolyte within the anolyte reservoir in a two-phasestream where the gas is allowed to separate from the liquid phase beforeexiting the reservoir via an anolyte reservoir gas outlet 56.

The anolyte reservoir 50 comprises an anolyte feed inlet 58 near thebottom. The anolyte feed inlet is connected to an anolyte feed inlettube 60 extending from and hydraulically connected to an anolyte make-uptank 62. The anolyte make-up tank comprises a closed container that isused to prepare and store the anolyte solution. The anolyte feed inlettube is connected to an anolyte discharge outlet 64 positioned at thebottom of the anolyte make-up tank. The anolyte solution is prepared byopening the container and inserting a predetermined amount of thedesired water-soluble chloride material, i.e., NaCl. The anolyte make-uptank comprises a fresh water inlet 66 positioned near the top of theanolyte make-up tank that is connected to a fresh water source. Ifdesired, a level control can be installed to control the delivery ofwater into the make-up tank to maintain a constant liquid level ofanolyte solution therein. The water-soluble chloride is dissolved intosolution by introducing fresh water into the anolyte make-up tank. It isdesired that the anolyte solution contained within the anolyte make-uptank be saturated. The specific gravity of a saturated NaCl isapproximately 1.19 to 1.20.

It has been discovered that the desired proportion of Cl₂ and ClO₂ gasmaking up the mixed oxidant gas can be obtained when the NaCl anolyte inthe anode chamber has a specific gravity of approximately 1.1, i.e., isnot saturated. The difference between the specific gravity of theanolyte in the anolyte make-up tank and the anolyte reservoir issufficient to cause gravity feeding of the anolyte solution from theanolyte make-up tank to the anolyte reservoir, via the anolyte feedinlet tube. The difference in specific gravity is sufficient to effectgravity feeding without need for increasing the pressure head of theanolyte in the anolyte make-up tank by either maintaining an anolytelevel above the anolyte level in the anolyte reservoir or raising theanolyte make-up tank above the anolyte reservoir.

It has also been discovered that the production of desired proportion ofCl₂ and ClO₂ gas occurs when there is observed conversion of thechloride ions (Cl⁻) in the anolyte to chlorite ion (ClO₂ ₋), which isthe precursor to ClO₂ gas. Accordingly, when the ClO₂ gas is generated,chlorite ion (ClO2⁻) is present in the anolyte. The presence of ClO2⁻ion in the anolyte as evidence of ClO₂ gas generation will be discussedin detail below.

It is desired to feed saturated NaCl solution to the anolyte reservoirto maintain the specific gravity of the NaCl solution in both theanolyte reservoir and anode chamber. As the electrolytic reactionproceeds in the anode chamber, the specific gravity of the anolytecontained within the anode chamber decreases due to production of Cl₂gas, and the liberation of Na+ ions and their migration across thepermeable membrane to the cathode chamber. The specific gravity of theanolyte in the anode chamber is maintained within the predeterminedrange by continuously introducing saturated NaCl anolyte solution fromthe anolyte make-up tank into the anolyte reservoir. The saturated NaClentering the anolyte reservoir serves to recharge or boost the specificgravity of the anolyte in the anolyte reservoir to the desired level forgenerating the preferred composition of the mixed oxidant gas.

A catholyte inlet 68 is positioned near the bottom of the cathode plateextending through the cathode plate to the cathode chamber. Like theanolyte inlet, the catholyte inlet can be attached to the cathode plateby use of the conventional connection means described above. Thecatholyte inlet port is threaded to accommodate threadable connectionwith a catholyte feed tube 70. A gas and catholyte outlet 72 is near thetop of the cathode plate extending through the cathode plate and intothe cathode chamber. The gas and catholyte outlet can be attached to thecathode by use of the same conventional connection means described abovefor the gas and anolyte outlet. The gas outlet port allows for both thecirculation of catholyte through the cathode chamber and the freedischarge of gases 73 generated in the cathode chamber from theelectrolytic cell. The gas outlet is threaded to accommodate threadableconnection with a gas transfer tube 74.

The catholyte is stored in a catholyte reservoir 76. The catholytereservoir comprises a sealed container accommodating a volume of thecatholyte. The catholyte reservoir and the cathode chamber may beconfigured so that the ratio of catholyte in the catholyte reservoir tothe catholyte in the cathode chamber is in the range of from 5,000:1 to1:1. In a first preferred embodiment, the catholyte reservoir has avolume of approximately one liter. Accordingly, in a first preferredembodiment, the ratio of the catholyte in the catholyte reservoir to thecatholyte in the cathode chamber is approximately 10:1.

The catholyte reservoir comprises a catholyte outlet 78 near the bottomof the reservoir that is always flooded with the catholyte. Thecatholyte outlet port is threaded for connection with the catholyte feedtube 70 connected to the cathode plate 30. The catholyte reservoircomprises a gas and catholyte inlet 80 near its upper end. The gas inletis threaded for connection with the gas transfer tube 74 connected tothe cathode plate 30. In a preferred embodiment, the gas inlet islocated a sufficient distance from the end of the catholyte reservoirthat it is below the liquid level of the catholyte in the reservoir. Itis desirable to place the gas inlet below the level of the catholyte tofacilitate both gas recovery from, and catholyte circulation through,the cathode chamber. The catholyte from the cathode chamber enters thecatholyte reservoir in a two-phase stream where the gas is allowed toseparate from the liquid phase before exiting the reservoir via acatholyte reservoir gas outlet 82 at the top of the catholyte reservoir.

In a preferred embodiment, the NaOH solution contained within thecatholyte reservoir has a specific gravity in the range of from about1.05 to 1.13. A catholyte having a specific gravity in this range, whenintroduced to the cathode chamber, has been shown to promote an optimumdegree of Na⁺ ion transfer from the anode chamber, through the permeablemembrane 26 and into the cathode chamber. The transfer of Na⁺ ions fromthe anode chamber into the cathode chamber promotes the optimum rate ofmixed oxidant gas, i.e., the electrolysis reaction in the anode chamberis driven to completion by the removal of the Na⁺ ions from the anodechamber. A catholyte having a specific gravity of less than about 1.05provides a concentration gradient across the permeable membrane 26greater than that required to effect the selected transfer of Na⁺ ionsthrough the permeable membrane 26. Rather, the large concentrationgradient produced by using a catholyte having a specific gravity of lessthan about 1.05 will result in the transfer of the anolyte ions, i.e.,NaCl, through the membrane, reducing the amount of mixed oxidant gasgenerated in the anode chamber. A catholyte having a specific gravity ofgreater than about 1.13 will not create the desired concentrationgradient across the permeable membrane to effect transfer of Na⁺ ionsfrom the anode chamber through the membrane, also reducing the amount ofmixed oxidant gas generated at the anode chamber.

As the NaOH catholyte from the catholyte reservoir enters the cathodechamber, the water molecules present in the solution undergoelectrolysis generating H₂ gas and OH⁻ ions. The OH⁻ ions and the Na⁺ions, transferred from the anode chamber through the permeable membrane,circulate through the cathode chamber and into the catholyte reservoirvia the gas transport tube 74. Accordingly, during the operation of theelectrolytic cell the concentration of Na⁺ and OH⁻ ions within thecatholyte reservoir increases, increasing the specific gravity of thecatholyte. To maintain the desired specific gravity of the catholyte inboth the cathode chamber and the catholyte reservoir, the catholytereservoir comprises a fresh water inlet 84 for diluting the catholyte bythe addition of water and a catholyte blow-down outlet (not shown) formaintaining the desired catholyte level and ridding the catholytereservoir of excess Na⁺ ion.

The catholyte reservoir may also comprise a water regulating means forregulating the amount of water entering the reservoir based on theparticular specific gravity of the catholyte. The water regulating meansmay comprise a hydrometer operated switch, such as a magnetic reedswitch, a hall effect transducer, a visual-type ultra-violet detectorand the like. In the first preferred embodiment the water regulatingmeans comprises a hydrometer 86 that, upon the specific gravity of thecatholyte rising above 1.13, rises to a level triggering a mechanismdischarging water from the fresh water inlet 84 into the catholytereservoir. As the fresh water enters the catholyte reservoir and thecatholyte level rises, excess Na⁺ ions are purged from the reservoir viathe catholyte blow-down outlet. Once the specific gravity of thecatholyte approaches the desired specific gravity range, the hydrometerlowers, shutting off the discharge of water into the reservoir. This isbut one embodiment of a means for regulating the specific gravity of thecatholyte in the catholyte reservoir. Accordingly, it is understood tobe within the scope of this invention that other means for regulatingthe specific gravity of the catholyte may also be used.

The electrolytic cell constructed according to principles of thisinvention produces a mixed oxidant gas comprising Cl₂ and ClO₂ in theanode chamber by applying a voltage differential in the range of fromthree to ten volts between the anode plate and cathode plate. Therelatively small volume of anolyte and catholyte contained within therespective anode and cathode chambers (approximately 100 milliliters ineach chamber), results in the electrolytic cell having a relatively lowinternal resistance. This reduced internal resistance, in turn, allowsthe cell to operate using only slightly more voltage than is necessaryto effect the desired electrolytic reactions in the anode and cathodechambers.

In the anode chamber, the NaCl is believed to undergo a number ofdifferent electrolytic reactions depending on the particular voltageapplied across the anode and cathode. While not wishing to be bound byany particular theory or mechanism, the NaCl in the anode chamber isbelieved to undergo electrolysis to form primarily Cl₂ and ClO₂ througha series of competing electrolytic reactions. One characteristic of thereactions is the presence of ClO₂ ⁻ ion in the anolyte generated by theseries of the competing electrolytic reactions. FIG. 5 illustrates anultra-violet spectrophotometric analysis of the anolyte circulatedthrough the anode chamber when the electrolytic cell constructedaccording to principles of this invention is operating at steady state,i.e., after approximately five minutes of operation at an appliedvoltage of approximately six volts and a current of approximately 40amperes. In FIG. 5, The presence of ClO₂ ⁻ ion is indicated by anabsorbance peak 85 at the wavelength of approximately 260 nanometers,the characteristic ultra-violet wavelength for ClO2- being approximately260 nanometers. Additionally, FIG. 4 also illustrates the presence ofClO₂ gas in the anolyte as indicated by an absorbance peak 87 at thewavelength of approximately 375 nanometers, the characteristicultra-violet wavelength for ClO₂ gas being approximately 375 nanometers.

A preferred ratio of ClO₂ to Cl₂ in the mixed oxidant gas isapproximately two to one. This ratio of ClO₂ to Cl₂ is desired becauseit has been found that a mixed oxidant gas having such ratio producesmore ClO₂ ⁻ and ClO₃ ⁻ ions in the body of water that the gas isinjected into, which serves to capture more calcium (Ca) ions in thewater to reduce scaling. Additionally, ClO₂ gas has the advantage ofbeing a longer lasting oxidant than Cl₂ gas. Although not as strong anoxidizing agent as hypochlorite (OCl⁻), ClO₂ is a moderate oxidizer thatis beneficial because it is both safer to handle and is not harmful toequipment that it may contact, such as piping, pumps, heat exchangers,and the like.

According to electrochemical principles, the NaCl solution is believedto first undergo electrolysis at a low voltage to form Na⁺ ions and Cl⁻ions. The Na⁺ ions travel from the anode chamber through the non-coatedportion of the permeable membrane 26 and enter the cathode chamber. Withincreasing voltage, the Cl⁻ ions combine with other Cl⁻ ions to form thedesired Cl₂ gas. With increasing voltage applied between the anode andcathode plate the Cl₂ gas reacts with H₂ O molecules in the anolyte toform HClO. With further increasing voltage the HClO reacts with H₂ Omolecules in the anolyte to form HClO₂. The amount of voltage necessaryto achieve this last reaction is obtained by applying a voltagedifferential across the anode plate and cathode plate in the range offrom about three to ten volts. Once the HClO₂ has been formed it reactsalmost instantaneously to form the desired ClO₂ gas, since the voltagenecessary to effect the electrolysis reaction forming the ClO₂ gas fromthe chlorite component of the HClO₂ is much lower than that necessary toform HClO₂.

These electrochemical principles are well supported by the operation ofthe electrolytic cell constructed according to principles of inventionsince. As shown in FIG. 5, during steady state operation the anolytecirculated through the anode chamber of the electrolytic cell is knownto comprise both ClO₂ gas and ClO₂ ⁻ ion, the precursor for ClO₂ gas.Additionally, the proportion of ClO₂ gas to Cl₂ gas produced by the cellis known to increase as the voltage applied between the anode plate andthe cathode plate is increased. Accordingly, if desired one could varyor regulate the desired proportion of ClO₂ gas to Cl₂ gas by varying thevoltage applied between the anode and cathode plate.

In determining the desired range for the voltage applied between theanode plate and cathode plate it was determined that the voltage shouldnot be so high as to produce, via electrolysis of H₂ O, H₂ O₂ or O₃since both of these molecules interfere with the production of ClO₂ gas.It was discovered that the minimum voltage applied between the anodeplate and cathode plate that would result in production of ClO₂ gas isgreater than approximately 4.25 volts, with ClO₂ gas being thepredominate gas produced in the anode chamber at approximately 6.25volts.

The NaOH solution entering the cathode chamber is believed to undergo aseries of electrolysis reactions whereby the H₂ O molecules of thecatholyte form OH⁻ ions and H₂ gas. Therefore, to drive the electrolyticreactions in the anode chamber to completion, the electrolytic reactionin the cathode chamber must also be driven to completion. Because of thestoichiometry of the electrolysis reaction at the cathode, as much asfive to six times more H₂ gas is created in the cathode chamber than theamount of mixed oxidant gas created in the anode chamber. Accordingly,to drive the electrolytic reactions in both the anode and cathodechamber to completion, a need exists to transport the H₂ gas from thecathode chamber as efficiently as possible.

The generation of H₂ gas in the cathode chamber causes bubbles to formin the catholyte volume during the operation of the electrolytic cell.As the bubbles are formed, they migrate through the catholyte, into avapor space 88 in the cathode chamber, as shown in the top portion ofFIG. 1. In order to promote the efficient collection of H₂ gas in thecathode chamber, the top portion of the open cavity in the cathodesealing gasket defining the vapor space may be convex. It is believedthat a vapor space having a generally triangular top promotes thecollection and transfer of H₂ gas from the cathode chamber.

Additionally, the diameter of the gas and catholyte outlet 72 and thegas transfer tube 74 may also be selected to both promote the efficientremoval of the H₂ gas from the cathode chamber and control the size ofthe H₂ gas bubbles. A small positive pressure maintained on the cathodechamber is desired because it promotes the formation of small H₂ gasbubbles, thereby minimizing the potential for an open circuit developingat the cathode surface.

The H₂ transferred to the catholyte reservoir is swept from thereservoir via the gas outlet 82 and may be vented to the atmosphere orcollected, stored and sold. To promote efficient electrolysis in thecathode chamber it is desired that the H₂ gas be removed from thecatholyte reservoir at a rate sufficient to maintain the migration ofthe H₂ bubbles through the cathode chamber. In a preferred embodiment,it is desirable that the rate of H₂ gas removal not exceed the rate ofH₂ gas generation so that a small amount of positive pressure ismaintained in the cathode chamber to control bubble size.

The catholyte in the catholyte reservoir 76 may be fed to the cathodechamber by a variety of transport means such as by gravity feed, pumpand the like. In a first preferred embodiment, the catholyte is fed bygravity. To ensure catholyte flow into the cathode chamber the catholytelevel in the catholyte reservoir is higher than the catholyte level inthe cathode chamber. A sufficient hydraulic head difference between thecatholyte in the catholyte reservoir and the catholyte in the cathodechamber can be obtained by raising the catholyte reservoir above theelectrolytic cell, as shown in FIG. 1. In a first preferred embodiment,a height difference of at least twenty-five millimeters is sufficient toprovide the desired hydraulic head difference.

The catholyte may be continuously circulated through the cathode chamberby the migration of H₂ gas bubbles (formed by electrolysis in thecathode chamber) upwards through the volume of the catholyte serving asa type of "catholyte lift," inducing the upwards circulation of thecatholyte. To maximize the ability of the migrating H₂ gas bubbles tocause the circulation of the catholyte through the cathode chamber it isdesired that the cathode plate be positioned close to the membrane plate20, and therefore close to the opposing anode plate. A desired degree ofcatholyte circulation is achieved when the cathode plate and the anodeplate are placed apart within the range of distances previouslydescribed.

The anolyte in the anolyte reservoir 50 may be fed to the anode chamberby a variety of transport means such as by gravity feed, pump and thelike. In a preferred embodiment, the anolyte in the anolyte reservoir isfed to the anode chamber by gravity. To ensure anolyte flow into theanode chamber the anolyte level in the anolyte reservoir is higher thanthat of the liquid level in the anode chamber. A sufficient hydraulichead difference between the anolyte in the anolyte reservoir and theanolyte in the anode chamber can be obtained by raising the anolytereservoir above the electrolytic cell, as shown in FIG. 1. In a firstpreferred embodiment, a height difference of at least twenty-fivemillimeters is sufficient to provide the desired hydraulic headdifference.

The anolyte may be continuously circulated through the anode chamber bythe migration of Cl₂ and ClO₂ gas bubbles (formed by electrolysis in theanode chamber) upwards through the volume of the anolyte serving as atype of "anolyte lift," inducing the upwards circulation of the anolyte.To maximize the ability of the migrating Cl₂ and ClO₂ gas bubbles tocause the circulation of the anolyte through the anode chamber it isdesired that the anode plate be positioned close to the membrane plate,and therefore close to the opposing cathode plate. A desired degree ofanolyte circulation is achieved when the anode plate and cathode plateare placed apart within the range of distances previously described.Additionally, the anolyte is circulated through the anode chamber bythermal convention via the release of thermal energy from theelectrolysis reactions occurring in the anode chamber.

The mixed oxidant gas transferred to the anolyte reservoir from theanode chamber migrates through the anolyte and is collected in the headspace of the anolyte reservoir. The collected gas is swept from theanolyte reservoir, via the mixed gas outlet 56, for introduction intothe body of water to be treated. In a preferred embodiment, the mixedgas outlet 56 is connected by tubing to a venturi (not shown) mounted inthe circulation piping for the water requiring treatment. The mixedoxidant gas enters the water by circulating the water through theventuri, causing the mixed oxidant gas to be swept from the anolytereservoir and injected into the water. Constructed in this manner, theelectrolytic cell may be used to inject the mixed oxidant gas intocirculation system of the water requiring treatment for maintaining alevel of mixed oxidant gas to provide the desired degree of protectionagainst biological activity, corrosion, and scaling.

It is desired that mixed oxidant gas be removed from the anolytereservoir at a rate slower than the rate at which the mixed oxidant gasis generated to maintain a small positive pressure in the anode chamber.Maintaining a small positive pressure in the anode chamber serves topromote the formation of small gas bubbles at the anode, minimizing thepotential for an open circuit developing at the anode surface.

The electrolytic reaction occurring in the anode chamber is known torelease a large amount of heat. This heat is ultimately transferred tothe anode plate and the anolyte which, if not removed, may eventuallycause the anolyte to boil. The boiling of the anolyte is not desiredbecause the formation of gas bubbles in the anolyte effectively reducesthe degree of contact between the anode plate and the anolyte,decreasing the efficiency of the electrolytic cell. The heat generatedin the anode chamber may be removed by using a variety of well knownthermal management devices such as a heat sink, e.g., mounted to thesurface of the anode plate, a heat exchanger, e.g., mounted in-line withthe anolyte circulation stream between the anode chamber and the anolytereservoir, and the like. In a preferred embodiment, the heat generatedin the anode chamber is controlled by routing a cooling water line 90into and through the anolyte reservoir for cooling the anolyte enteringthe anode chamber, as shown in FIG. 1.

In a first preferred embodiment, a voltage of approximately six volts issufficient to provide a desired current of from about 15 to 50 ampsthrough the cell. It has been found that an electrolytic cell with thedimensions described above and operated at approximately 40 amps,generates a sufficient amount of mixed oxidant gas to effectivelycontrol biological activity, corrosion, and scaling in industrial waterapplications equivalent to a 1500 ton cooling tower.

After the predetermined voltage is applied between the anode and cathodeplates the electrolysis reactions begin in both the anode and cathodechamber. It has been found that the desired rate and proportion of Cl₂and ClO₂ gas is generated in the anode chamber after approximately fiveminutes, reflecting the time for the electrochemical system to achieveequilibrium. The ability to achieve equilibrium after only a relativelyshort period is due to the construction of the electrolytic cell, i.e.,the small working electrolyte volume in the anode and cathode chambers.

The time for achieving equilibrium may be reduced by preserving theequilibrium state of the anolyte and catholyte in the anode and cathodechamber, respectively, after the electrolytic cell has been shut off. Ifdesired, the equilibrium state of the anolyte and catholyte may bepreserved by installing valves (not shown) in both the mixed gastransfer tube 48 and the gas transfer tube 74. By closing these valvesafter the operation of the electrolytic cell, the mixed oxidant gas andthe H₂ gas are retained within the respective cathode and anode chamber.Retaining the gases within each chamber serves to decrease the timeneeded to achieve equilibrium because the desired gas species arealready present. Alternatively, such valves may be installed in theanolyte reservoir gas outlet 56 and the gas outlet 82 to yield similarresults. By using such valves, the time necessary to achieve equilibriumupon start up may be decreased by as much as 75 percent.

The electrolyte cell having an anolyte and catholyte reservoir externalto the respective anode and cathode chamber has several distinctadvantages over electrolytic cells comprising integral reservoirs andchambers. The use of external electrolyte reservoirs permits theconstruction of an electrolytic cell having an anode and cathode chamberof reduced electrolyte volume, reducing the internal resistance of theelectrolytic cell and increasing the electrical efficiency of theelectrolytic cell. The use of external electrolyte reservoirsfacilitates convenient maintenance and service of the electrolytic cellbecause the cell is both smaller and less complicated to work with. Theuse of external electrolyte reservoirs allows for the mixed oxidant gasto be drawn from the anolyte reservoir, and not the anode chamber whereit is desirable that the equilibrium state not be upset, in order topromote efficient mixed oxidant gas generation. Accordingly, theexternal anolyte reservoir acts as a type of buffer, minimizingpotential equilibrium upsets in the anode chamber.

Because of their large volume relative to the respective anode andcathode chambers, the anolyte and catholyte reservoirs act as a bufferto minimize specific gravity swings from occurring within each chamber.The approximately 10:1 volume difference, for the first preferredembodiment, between each reservoir and its respective cell chamberserves to buffer the electrolyte entering each cell chamber from theeffects of the electrolytic process occurring in each chamber.Accordingly, using the external anolyte and catholyte reservoir allowseach cell chamber to receive electrolyte having a constant predeterminedcomposition, optimizing the ability of the cell to generate the desiredcomposition and quantity of mixed oxidant gas.

Although limited embodiments of the electrolytic cell have beendescribed herein, many modifications and variations will be apparent tothose skilled in the art. For example, it is to be understood within thescope of invention that the electrolytic cell may be constructedincorporating the use of a bipolar electrode. FIG. 6 illustrates anembodiment of an electrolytic cell comprising a bipolar electrode 92interposed between the anode plate 14 and the membrane plate 20. In suchan embodiment the bipolar electrode may be used to improve the yield ofthe desired proportion of ClO₂ and Cl₂ gas via electrolysis in the anodechamber.

The bipolar electrode may be made from a structurally rigid materialthat is both chemically resistant to the anolyte and electrochemicallyresistant to the electrolysis reactions occurring in the anode chamber.Additionally, it is desirable that the bipolar electrode comprise aplurality of openings through its surface to facilitate the circulationof the anolyte through the anode chamber. It is desirable that bothsides of the bipolar electrode comprise an electrically conductivecoating to promote the desired electrolysis reactions in the anodechamber. Suitable conductive coatings include the same types ofmaterials previously described for coating the anode plate. In apreferred embodiment, incorporating the use of a bipolar electrode, abipolar electrode is made from expanded titanium and coated with aniridium material produced by Eltech of Chardon, Ohio, under the productname EC600.

FIG. 7 illustrates an embodiment of the anode sealing gasket 14previously described comprising a bipolar electrode 92 extending acrossa portion of the open cavity 16. The bipolar electrode may be retainedwithin the open cavity of the anode sealing gasket by a tongue andgroove arrangement or the like. The bipolar electrode may extend acrossand cover the entire open cavity 16 or may only partially extend acrossthe open cavity. It has been discovered that the optimum production ofthe desired mixed oxidant gas is obtained by installing the bipolarelectrode in the top half of the anode sealing gasket, as shown in FIG.7. It is to be understood that the embodiment of the anode sealinggasket plate illustrated in FIG. 7 is similar in all respects to theanode sealing gasket previously described and illustrated in FIG. 3except for the installation of the bipolar electrode.

FIG. 8 illustrates a second preferred embodiment of an electrolytic cellconstructed according to principles of this invention. The secondpreferred embodiment of the electrolytic cell 94 is similar to the firstpreferred embodiment of the electrolytic cell described above andillustrated in FIG. 1, comprising an anolyte reservoir 96 external fromand hydraulically connected to an anode chamber 98 of the cell, ananolyte make-up tank 100 external from and hydraulically connected tothe anolyte reservior 96, and a catholyte reservior 102 external fromand hydraulically connected to a cathode chamber 104 of the cell. Theelectrolytic cell is configured in identically the same manner as thatpreviously described and illustrated for the first preferred embodiment.

The Second preferred embodiment of the electrolytic cell is differentfrom the first embodiment in that the catholyte reservoir 102 includes aspecific gravity sensor 106 in the form of a magnetic reed switch, thatoperates to regulate the dispensement of fresh water into the catholytereservoir by allowing the flow of water into the catholyte reservoirwhen the specific gravity of the catholyte reaches a predeterminedvalue, and closing off the fresh water flow to the catholyte reservoirwhen the specific gravity concentration returns to a predeterminedvalue. The catholyte reservoir also includes a catholyte cooling meansin the form of a cooling coil 106 disposed therein, for maintaining thetemperature of the catholyte within a predetermined temperature window.The cooling medium displaced through the cooling coil can include waterin the form of either the host water that is being treated by the cellor make-up water, whichever one is at the desired cooling temperature.In a preferred embodiment, it is desired that the catholyte containedwithin the catholyte reservoir be maintained within a temperature rangeof from 65° to 90° F.

Additionally, the second embodiment of the electrolytic cell differsfrom the first embodiment in the both the anolyte and catholytereservoirs 96 and 102, respectively, are sized having a increased volumeof approximately 3 liters. The increase in reservoir volume accommodatesa larger volume of catholyte and anolyte that can be cooled, which inturn serves as a heat sink to minimize fluctuations in the temperatureof anolyte or catholyte entering the respective anode and cathodechamber. The increase in anolyte and catholyte volume within eachrespective anolyte and catholyte reservoir also helps to reduce theextent of specific gravity changes to the anolyte and catholyte in eachrespective reservoir due to the electrochemical reactions occurringwithin the anode and cathode chambers of the cell; thereby, facilitatingsmooth and uninterrupted operation of the cell.

Additionally, the second embodiment of the electrolytic cell differsfrom the first embodiment in that the anolyte reservoir includes aspecific gravity sensor 110 of the same type previously described forthe catholyte reservoir. The specific gravity sensor operates to speedup the activation of an anolyte metering pump 112 having its inlet endconnected to the anolyte feed inlet tube 114, extending from the anolytedischarge outlet 116 positioned at the bottom of the anolyte make-uptank 100, and having its outlet end connected to the anolyte feed inlettube 118 extending to the bottom of the anolyte reservoir 96. The pump112 feeds the saturated NaCl solution stored in the anolyte make-up tank100 to the anolyte reservoir 96 in a metered quantity, according to theamount of anolyte solution exhausted by the electrolytic cell 94 duringoperation. In a second preferred embodiment, the pump 112 is configuredto dispense saturated anolyte solution to the anolyte reservoir at aflow rate in the range of from 0.1 to 0.6 liters per 24 hours (0.5 to 2gallons per day). It is to be understood, however, that the selecteddispensment rate of anolyte solution is dependent on many variables suchas the voltage applied between the plates, the condition of thepermeable membrane, the specific gravity of the anolyte solution, etc.,and, therefore, is understood to vary from this range.

The specific gravity sensor 110 operates to increase and/or decrease themetering rate of the pump 112 according to the specific gravity value ofthe anolyte contained within the anolyte reservoir 96 so that apredetermined specific gravity value is maintained. For example, if thesensor detects that the specific gravity of the anolyte is below apredetermined value, the pump is activated to increase the metering rateof anolyte. Conversely, if the sensor detects that the specific gravityof the anolyte is above a predetermined value, the pump is activated todecrease the metering rate of the anolyte. Although a specific form ofspecific gravity sensor has been described and illustrated for use inthe second preferred cell embodiment, it is to be understood that othertypes of sensors, as previously decried for the first preferredembodiment, can be used.

Additionally, the second embodiment of the electrolytic cell may includea water regulating means (not shown) installed in the anolyte make-uptank 100 in the form of a float valve or the like that operates tomaintain the liquid level of saturated anolyte solution within the tankat a predetermined level by regulating the dispensement of fresh watertherein.

FIG. 9 illustrates a first preferred multi-electrolytic cell embodiment122 comprising five electrolytic cells 124 constructed according toprinciples of this invention. Each electrolytic cell 124 is identical toeach other electrolytic cell, and is constructed in the same manner, andhaving the same dimensions, as that previously described and illustratedfirst preferred electrolytic cell embodiment. The anolyte inlet 126extending from the anode plate 128 of each cell is hydraulicallyconnected in parallel to an anolyte feed manifold 130, which in turn ishydraulically connected, via an anolyte transfer tube 132 to the anolyteoutlet 134 of the anolyte reservoir 136. Anolyte is dispensed inparallel flow to the anode chamber of each cell from the anolytereservoir 136 via the transfer tube 132 and the manifold 130.

The mixed gas outlet 140 extending from the anode plate 128 of each cellis hydraulically connected in parallel to a mixed gas manifold 142,which in turn is hydraulically connected, via a mixed gas transfer tube146 to the mixed gas and anolyte inlet 146 of the anolyte reservoir.Mixed gas is transferred from the anode chamber of each cell in parallelflow to the anolyte reservoir 136 via the transfer tube 144 and themanifold 142.

The catholyte inlet 148 extending from the cathode plate 150 of eachcell is hydraulically connected in parallel to a catholyte feed manifold152, which in turn is hydraulically connected, via a catholyte transfertube 154 to the catholyte outlet 156 of the catholyte reservoir 158.Catholyte is dispensed in parallel flow to the cathode chamber of eachcell from the catholyte reservoir 158 via the transfer tube 154 and themanifold 152.

The gas and catholyte outlet 162 extending from the cathode plate 150 ofeach cell is hydraulically connected in parallel to a gas and catholytemanifold 164, which in turn is hydraulically connected, via a gas andcatholyte transfer tube 166 to the gas and catholyte inlet 168 of thecatholyte reservoir 158. Gas and catholyte is transferred from thecathode chamber of each cell in parallel flow to the catholyte reservoir158 via the transfer tube 166 and the manifold 164.

The anolyte and catholyte reservoirs 136 and 158, respectively, are eachsized having a volume greater than that previously described for thefirst and second preferred single cell embodiments, to facilitate theincreased anode and cathode chamber volume, and to accommodate theincreased exhaustion rate of the anolyte and catholyte, associated withusing multiple electrolytic cells. In a preferred first multi-cellembodiment, the anolyte and catholyte reservoir each has a volume ofapproximately 22 liters. An anolyte and catholyte reservoir configuredhaving such a volume accommodates a volume of anolyte and catholyte thatacts as a heat sink to provide better anolyte and catholyte temperaturecontrol, and acts buffer the effects of specific gravity changesinherent in the electrochemical reactions occurring in both the anodeand cathode chamber of each cell.

The anolyte and catholyte chamber 136 and 158, respectively, are eachconfigured in the same manner as previously described and illustratedfor the second preferred single cell embodiment, each comprising acooling coil 170 and 172, and a specific gravity sensor 174 and 176. Thespecific gravity sensors that are used with each respective anolyte andcatholyte reservoir serve the same function as that previously describedfor the second preferred single cell embodiment, i.e., to regulate themetered flow of saturated anolyte solution from the anolyte make-up tank(not shown) to the anolyte reservoir 136 via the anolyte metering pump178 and the anolyte feed inlet 180, and to regulate the dispensment offresh water into the catholyte reservoir 158 via fresh water inlet 182.In the first preferred multi-cell embodiment, the metering pump 178 isconfigured to dispense saturated anolyte solution to the anolytereservoir in the range of from 0.2 to 1.1 liters per 24 hours (1 to 4gallons per day).

The electrolytic cells 124 of the first preferred multi-cell embodimentare electrically connected in parallel and are operated to generate themixed oxidant gas by applying a total voltage of approximately 30 voltsacross the cells, which provides a voltage of approximately 6 voltsacross the anode and cathode of each cell. Application of 30 volts issufficient to provide a desired total current of from about 75 to 250amps through the cells, or a current of from about 15 to 50 amps througheach cell. The first preferred multi-cell embodiment constructedaccording to principles of this embodiment generates a quantity of mixedoxidant gas that is approximately five times that of a singleelectrolytic cell and, therefore, can be used in one application totreat a 7,500 ton cooling tower.

FIG. 11 illustrates a second preferred multi-cell embodiment 184comprising five electrolytic cells 186. The second preferred multi-cellembodiment is same as the first preferred multi-cell embodimentdisclosed above with the exception that manifolds 130, 142, 152 and 164are not used to facilitate the transport of anolyte, mixed gas,catholyte, and gas and catholyte, respectively, from the anode chamberand cathode chamber of each cell. Rather, the anolyte is supplied to theanode chamber of each cell 186 by an independent anolyte transport tube190 that is hydraulically connected at one end to the anolyte inlet 192extending from the anode plate 194, and is connected at an opposite endto an anolyte outlet 196 in the anolyte reservoir 198. The anolytereservoir 198 is configured having an equal number of independentanolyte outlets 196 to accommodate hydraulic connection with the anolyteinlet 192 of each cell, thereby, eliminating the need for an anolytefeed manifold.

The mixed gas outlet 200 extending from the anode plate 194 of each cellis hydraulically connected via a mixed gas transport tube 202 to a mixedgas inlet 204 of the anolyte reservoir. The anolyte reservoir 198 isconfigured having an equal number of independent mixed gas inlets 204 toaccommodate hydraulic connection with the mixed gas outlet 200 of eachcell, thereby, eliminating the need for a mixed gas manifold.

In the second preferred multi-cell embodiment, the catholyte is suppliedto the cathode chamber of each cell 186 by a catholyte transport tube208 that is hydraulically connected at one end to the catholyte inlet(not shown) extending from the cathode plate 212, and is connected at anopposite end to a catholyte outlet 214 in the catholyte reservoir 216.The catholyte reservoir 216 is configured having an equal number ofindependent catholyte outlets 214 to accommodate hydraulic connectionwith the catholyte inlet 210 of each cell, thereby, eliminating the needfor a catholyte feed manifold.

The gas and catholyte outlet (not shown) extending from the cathodeplate 212 of each cell is hydraulically connected via a gas andcatholyte transport tube 220 to a gas and catholyte inlet 222 of thecatholyte reservoir. The catholyte reservoir 216 is configured having anequal number of independent gas and catholyte inlets 222 to accommodatehydraulic connection with the gas and catholyte outlet of each cell,thereby, eliminating the need for a gas and catholyte manifold.

The electrolytic cells, anolyte reservoir, catholyte reservoir, anolytemake-up tank (not shown), and saturated anolyte metering pump are eachconfigured in the same manner as previously described for the firstpreferred multi-cell embodiment. Additionally, the electrolytic cells inthe second preferred multi-cell embodiment are, like the first preferredmulti-cell embodiment, also electrically connected in parallel and are,therefore, operated in the same manner, i.e., applying a total voltageof approximately 30 volts and in the range of from 75 to 250 total ampsacross the five cells, or approximately 6 volt from 15-50 amps acrosseach cell, to produce the desired mixed oxidant gas.

Although first and second preferred multi-cell embodiments have beenspecifically described and illustrated comprising five electrolyticcells, it is to be understood that the number of individual electrolyticcells constructed according to principles of this invention that can becombined to in accordance with this invention is not means to belimited. For example, greater or fewer than five electrolytic cells maybe combined to provide a generation rate of the mixed oxidant gassufficient to meet the treatment needs in particular application.

Alternatively, it is to be understood that rather than using multipleelectrolytic cells to increase the generation rate of the mixed oxidantgas, a single electrolytic cell of enlarged dimension can be constructedin accordance with principles of this invention. Accordingly, forexample, a single cell having five times the surface area of the firstand second preferred single cell embodiments could be used to provideapproximately the same generation rate of mixed oxidant gas as the firstand second preferred multi-cell embodiments comprising five cells. Thechoice of whether to construct a single enlarged cell or to combine amultiple number of smaller cells is ultimately a decision that is drivenby any space constraint for the electrolytic cell(s) and any differencein manufacturing cost.

Accordingly, it is to be understood that, within the scope of theappended claims, the electrolytic cell constructed according toprinciples of invention may be embodied other than as specificallydescribed herein.

What is claimed is:
 1. At least one electrolytic cell for generating amixed oxidant gas for treating bodies of water, each cell comprising:ananode chamber defined by an anode plate at one end, a permeable membraneat an opposite end, and a first sealing gasket interposed therebetween;a cathode chamber adjacent the anode chamber defined by a cathode plateat one end, the permeable membrane at an opposite end, and a secondsealing gasket interposed therebetween, the first and second gasketsbeing separated by the permeable membrane; an anolyte reservoir externalfrom the anode chamber for accommodating a volume of anolyte therein,wherein the anolyte reservoir is connected to the anode chamber tocirculate anolyte thereto and to receive mixed oxidant gas therefrom; acatholyte reservoir external from the cathode chamber for accommodatinga volume of catholyte therein, wherein the catholyte reservoir isconnected to the cathode chamber to circulate catholyte thereto and toreceive gas therefrom; means for maintaining the anolyte containedwithin the anolyte reservoir at a controlled specific gravity; aspecific gravity sensor disposed within the catholyte reservoir thatwhen activated causes water to be dispensed into the catholyte reservoirto maintain a controlled catholyte specific gravity therein.
 2. Theelectrolytic cell as recited in claim 1 comprising an anolyte make-uptank external from the anolyte reservoir and anode chamber forcontaining a volume of saturated anolyte therein, wherein the anolytemake-up tank is connected to the anolyte reservoir to facilitatesaturated anolyte transport thereto.
 3. The electrolytic cell as recitedin claim 2 comprising a pump connected between the anolyte make-up tankand anolyte reservoir to dispense saturated anolyte solution to anolytereservoir.
 4. The electrolytic cell as recited in claim 3 wherein themeans for maintaining the anolyte within the anolyte reservoir at thecontrolled specific gravity comprises a specific gravity sensor disposedwithin the anolyte reservoir that when activated adjusts the flow rateof the pump.
 5. The electrolytic cell as recited in claim 1 comprising anumber of electrolytic cells, wherein the anode chamber of each cell isconnected to a common anolyte reservoir external from the anode chamberto effect anolyte transport from the anolyte reservoir to the anodechamber, and to effect transport of mixed gas and anolyte from the anodechamber to the anolyte reservoir.
 6. The electrolytic cell as recited inclaim 5 comprising a number of electrolytic cells, wherein the cathodechamber of each cell is connected to a common catholyte reservoirexternal from the cathode chamber to effect catholyte transport from thecatholyte reservoir to the cathode chamber, and to effect transport ofgas and catholyte from the cathode chamber to the catholyte reservoir.7. At least one electrolytic cell for generating a mixed oxidant gascomprising:an anode plate; a cathode plate opposite to the anode plate;a permeable membrane interposed between the anode plate and the cathodeplate; an anode sealing gasket interposed between the anode plate andthe permeable membrane forming an anode chamber for accommodating avolume of anolyte; a cathode sealing gasket interposed between thecathode plate and the permeable membrane forming a cathode chamber foraccommodating a volume of catholyte; an anolyte reservoir external fromand hydraulically connected to the anode chamber for circulating anolyteat a specific gravity to the anode chamber and for receiving a mixedoxidant gas from the anode chamber; an anolyte make-up tank externalfrom the anolyte reservoir and anode chamber and hydraulically connectedto the anolyte reservoir for providing saturated anolyte to the anolytereservoir; means for transporting saturated anolyte from the anolytemake-up tank to the anolyte reservoir; and a catholyte reservoirexternal from and hydraulically connected to the cathode chamber forcirculating catholyte to the cathode chamber and for receiving gas fromthe cathode chamber.
 8. The electrolytic cell as recited in claim 7comprising means for regulating fresh water dispensement to thecatholyte reservoir to keep the catholyte within the catholyte reservoirat a controlled specific gravity.
 9. The electrolytic cell as recited inclaim 7 wherein the means for transporting saturated anolyte solutioncomprises a pump installed between the anolyte make-up tank and theanolyte reservoir.
 10. The electrolytic cell as recited in claim 9wherein the anolyte reservoir comprises a sensor that monitors thespecific gravity of the anolyte within the anolyte reservoir increasesthe flow rate of the pump when the specific gravity is below acontrolled value.
 11. The electrolytic cell as recited in claim 7wherein the anolyte reservoir comprises a cooling coil to temperaturecondition the anolyte contained therein.
 12. The electrolytic cell asrecited in claim 7 wherein the catholyte reservoir comprises a coolingcoil to temperature condition the catholyte contained therein.
 13. Theelectrolytic cell as recited in claim 7 comprising a bipolar electrodedisposed within the anode chamber.
 14. The electrolytic cell as recitedin claim 7 comprising a number of electrolytic cells, wherein the anodeand cathode chamber of each cell are hydraulically connected to theanolyte and catholyte reservoir for transporting anolyte to andreceiving mixed gas from each anode chamber, and for transportingcatholyte to and receiving gas from each cathode chamber.
 15. Theelectrolytic cell as recited in claim 14 comprising an anolyte manifoldconnected between each anode chamber and the anolyte reservoir tofacilitate the transport of the anolyte, and comprising a catholytemanifold connected between each cathode chamber and the catholytereservoir to facilitate the transport of the catholyte.
 16. Theelectrolytic cell as recited in claim 15 comprising a mixed gas manifoldconnected between each anode chamber and the anolyte reservoir tofacilitate transport of the mixed gas and anolyte, and comprising a gasand catholyte manifold connected between each cathode chamber thecatholyte reservoir to facilitate transport of the gas and catholyte.17. The electrolytic cell as recited in claim 14 wherein the anolytereservoir comprises a sufficient number of individual anolyte outletports to accommodate hydraulic connection with a respective anodechamber of each cell to provide anolyte transfer thereto, and whereinthe catholyte reservoir comprises a sufficient number of individualcatholyte outlet ports to accommodate hydraulic connection with arespective cathode chamber of each cell to provide catholyte transferthereto.
 18. The electrolytic cell as recited in claim 17 wherein theanolyte reservoir comprises a sufficient number of individual mixed gasinlet ports to accommodate hydraulic connection with the anode chamberof each cell to provide mixed gas transfer therefrom, and wherein thecatholyte reservoir comprises a sufficient number of individual gas andcatholyte inlet ports to accommodate connection with the cathode chamberof each cell to provide gas and catholyte transfer therefrom.
 19. Atleast one electrolytic cell for generating a mixed oxidant gas fortreating bodies of water, each cell comprising:an anode plate; an anodesealing gasket disposed adjacent to a surface of the anode plate; apermeable membrane disposed adjacent to a surface of the anode sealinggasket opposite from the anode plate, wherein the anode plate, anodesealing gasket and membrane form an anode chamber therebetween foraccommodating a volume of anolyte; a cathode sealing gasket disposedadjacent to a surface of the permeable membrane opposite from the anodesealing gasket; a cathode plate disposed adjacent to a surface of thecathode sealing gasket opposite from the permeable membrane, wherein thecathode plate, cathode sealing gasket and membrane form a cathodechamber for accommodating a volume of catholyte; a bipolar electrodeinterposed between the anode plate and the permeable membrane; ananolyte reservoir for accommodating a volume of anolyte external fromthe anode chamber, wherein the anolyte reservoir is hydraulicallyconnected to the anode chamber to circulate anolyte thereto and receivemixed oxidant gas therefrom, and wherein the anolyte reservoir includesmeans for maintaining anolyte contained therein at a controlled specificgravity; and a catholyte reservoir for accommodating a volume ofcatholyte external from the cathode chamber, wherein the catholytereservoir is hydraulically connected to the cathode chamber to circulatecatholyte thereto and receive gas therefrom, and wherein the catholytereservoir includes means for maintaining catholyte contained therein ata controlled specific gravity.
 20. The electrolytic cell as recited inclaim 19 comprising an anolyte make-up tank for accommodating a volumeof saturated anolyte external from the anolyte reservoir and anodechamber, wherein the anolyte make-up tank is hydraulically connected tothe anolyte reservoir to effect anolyte transport thereto.
 21. Theelectrolytic cell as recited in claim 20 comprising a pump installedbetween the anolyte make-up tank and anolyte reservoir configured todispense saturated anolyte to the anolyte reservoir.
 22. Theelectrolytic cell as recited in claim 21 wherein the means formaintaining the anolyte at a controlled specific gravity comprises aspecific gravity sensor that when activated is configured to adjust theflow rate of the pump.
 23. The electrolytic cell as recited in claim 19wherein the means for maintaining the catholyte at a controlled specificgravity comprises a specific gravity sensor that when activatedregulates the dispensement of fresh water into the catholyte reservoir.24. The electrolytic cell as recited in claim 19 wherein the anolytereservoir comprises means for temperature conditioning the anolytecontained therein.
 25. The electrolytic cell as recited in claim 19wherein the catholyte reservoir comprises means for temperatureconditioning the catholyte contained therein.
 26. The electrolytic cellas recited in claim 19 comprising a number of electrolytic cells,wherein the anode chamber of each cell is connected to a common anolytereservoir external from the anode chamber to effect anolyte transportfrom the anolyte reservoir to each anode chamber, and to effecttransport of mixed gas and anolyte from each anode chamber to theanolyte reservoir.
 27. The electrolytic cell as recited in claim 26comprising a number of electrolytic cells, wherein the cathode chamberof each cell is connected to a common catholyte reservoir external fromthe cathode chamber to effect catholyte transport from the catholytereservoir to each cathode chamber, and to effect transport of gas andcatholyte from each cathode chamber to the catholyte reservoir.